A smooth onset of collectivity in 88, 92,94,96 Kr has been determined from reported B (E2;2+1→0+1) and E(2+1) values. This is in contrast to the sudden onset in even-even Zr, Mo, and Sr isotopes. Our objective was to complete the systematics by determining the B (E2;2+1→0+1) value in 90Kr, which was produced by cold-neutron-induced fission of 235U. The lifetime of the 2+1state in 90 Kr was measured via the electronic γ−γ timing technique using the EXILL and FATIMA spectrometers. Based on the measured mean lifetime of τ = 15(10)ps, the B(E2;2+1→0+1) value of 13+26−5 W.u. in 90 Kr is determined for the first time and the smooth onset of deformation in the even-even Kr isotopes beyond neutron number N=50 is confirmed.